Trigonometry: Sum, Difference and Product Identities

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Questions and Answers

Which of the following expressions is equivalent to $sin(3\alpha)$?

  • $3sin(\alpha) + 4sin^3(\alpha)$
  • $4sin(\alpha) - 3sin^3(\alpha)$
  • $3sin(\alpha) - 4sin^3(\alpha)$ (correct)
  • $4sin(\alpha) + 3sin^3(\alpha)$

Given $cos(\alpha) = \frac{1}{4}$, find the value of $cos(3\alpha)$.

  • $-\frac{47}{64}$ (correct)
  • $\frac{47}{64}$
  • $-\frac{11}{16}$
  • $\frac{11}{16}$

Simplify the expression: $2sin(x)cos(3x)$

  • $sin(4x) + sin(2x)$
  • $cos(4x) - cos(2x)$
  • $sin(4x) - sin(2x)$ (correct)
  • $cos(4x) + cos(2x)$

If $tan(\alpha) = 2$ and $tan(\beta) = \frac{1}{3}$, find the value of $tan(\alpha + \beta)$.

<p>$\frac{7}{5}$ (B)</p> Signup and view all the answers

Given $sin(\alpha) = \frac{3}{5}$ and $cos(\beta) = \frac{5}{13}$, where both $\alpha$ and $\beta$ are in the first quadrant, find the value of $cos(\alpha - \beta)$.

<p>$\frac{56}{65}$ (A)</p> Signup and view all the answers

Which of the following is equivalent to $cos(2x)$?

<p>$cos^2(x) - sin^2(x)$ (A)</p> Signup and view all the answers

What is the simplified form of the expression $\frac{1 - cos(2\theta)}{sin(2\theta)}$?

<p>$tan(\theta)$ (C)</p> Signup and view all the answers

Determine the expression equivalent to $sin(x + \frac{\pi}{2})$.

<p>$cos(x)$ (A)</p> Signup and view all the answers

If $tan(\theta) = -\frac{3}{4}$ and $\theta$ is in the second quadrant, find the value of $sin(2\theta)$.

<p>$-\frac{24}{25}$ (D)</p> Signup and view all the answers

Simplify: $cos(\frac{\pi}{2} - \theta)$

<p>$sin(\theta)$ (B)</p> Signup and view all the answers

Flashcards

sin(α + β) Identity

sin(α + β) = sinα cosβ + cosα sinβ

cos(α + β) Identity

cos(α + β) = cosα cosβ - sinα sinβ

tan(α + β) Identity

tan(α + β) = (tanα + tanβ) / (1 - tanα tanβ)

sin(2α) Identity

sin(2α) = 2sinα cosα

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cos(2α) Identity

cos(2α) = cos²α - sin²α = 2cos²α - 1 = 1 - 2sin²α

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tan(2α) Identity

tan(2α) = (2 tanα) / (1 - tan²α)

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sin(3α) Identity

sin(3α) = 3sinα - 4sin³α.

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cos(3α) Identity

cos(3α) = 4cos³α - 3cosα.

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tan(3α) Identity

tan(3α) = (3tanα - tan³α) / (1 - 3tan²α)

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sin(-θ) Identity

sin(-θ) = -sin(θ)

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Study Notes

  • Trigonometry study notes

Sum/Differences identities

  • sin(α+β) = sinα cosβ + cosα sinβ
  • sin(α-β) = sinα cosβ - cosα sinβ
  • cos(α+β) = cosα cosβ - sinα sinβ
  • cos(α-β) = cosα cosβ + sinα sinβ
  • tan(α+β) = (tan α + tan β) / (1 - tanα tan β)
  • tan(α-β) = (tanα - tan β) / (1 + tanα tan β)
  • cot(α+β) = (cotα cotβ - 1) / (cot β+ cot α)
  • cot(α-β) = (cotα cotβ + 1) / (cot β - cot α)

Double angle identities

  • cos 2α = cos² α - sin² α
  • cos 2α = 1 - 2sin² α which implies 2sin² α = 1 - cos² α
  • cos 2α = 2cos² α - 1, and 1 + cos2α = 2 cos² α
  • sin²(α/2) = (1 - cosα) / 2
  • tan 2α = (2 tan α) / (1 - tan² α)
  • cos 2α = (1 - tan² α) / (1 + tan² α)
  • sin 2α = (2 tan α) / (1 + tan² α)

Triple angle identities

  • sin3α = 3sinα - 4sin³ α
  • cos3α = 4cos³α - 3 cosα
  • tan3α = (3 tanα - tan³ α) / (1 - 3 tan² α)

Product to sum identities

  • 2sinα cosβ = sin(α+β) + sin(α-β)
  • 2cosα sinβ = sin(α+β) - sin(α-β)
  • 2cosα cosβ = cos(α+β) + cos(α-β)
  • 2sinα sinβ = cos(α-β) - cos(α+β)

Sum to product identities

  • sinα + sinβ = 2sin((α+β)/2) cos((α-β)/2)
  • sinα - sinβ = 2cos((α+β)/2) sin((α-β)/2)
  • cosα + cosβ = 2cos((α+β)/2) cos((α-β)/2)
  • cosα - cosβ = -2cos((α+β)/2) sin((α-β)/2)

Other identities

  • sin² α - sin² β = sin(α+β)·sin(α-β)
  • cos² α - cos² β = sin(β+α)·sin(β-α)

Even/Odd identities

  • sin(-θ) = -sinθ
  • cos(-θ) = cos θ
  • tan(-θ) = -tan θ
  • cosec(-θ) = -cosec θ
  • sec(-θ) = sec θ
  • cot(-θ) = -cot θ

Confunction identities

  • sin(π/2 - θ) = cos θ
  • cosec(π/2 - θ) = sec θ
  • tan(π/2 - θ) = cot θ
  • cot(π/2 - θ) = tan θ
  • sec(π/2 - θ) = cosec θ
  • cot(π/2 - θ) = tan θ

Half Angle identities

  • sin(θ/2) = ±√((1 - cos θ)/2)
  • cos(θ/2) = ±√((1 + cos θ)/2)
  • tan(θ/2) = ±√((1 - cos θ)/(1 + cos θ))

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